Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$139.36	7.797%	$150.2259	$150.23	$150.25	$150.20
Purchase #2	$31.52	13.708%	$35.8408	$35.84	$35.85	$35.80
Purchase #3	$160.80	5.837%	$170.1859	$170.19	$170.20	$170.20
Purchase #4	$92.52	8.547%	$100.4277	$100.43	$100.45	$100.40
Purchase #5	$24.52	4.559%	$25.6379	$25.64	$25.65	$25.60
Purchase #6	$96.25	13.759%	$109.493	$109.49	$109.50	$109.50
Purchase #7	$13.48	10.136%	$14.8463	$14.85	$14.85	$14.80
7 purchase totals =	$558.45		$606.6575	$606.67	$606.75	$606.50